Construction hardware and method of reducing corrosion thereof

ABSTRACT

A method of reducing corrosion in an article of construction hardware resulting from exposure to ACQ treated lumber and an article of construction hardware treated in accordance with such method.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to construction hardware and amethod for reducing the corrosion thereof. More specifically, thepresent invention relates to construction hardware and the like whichhave been manufactured from coil steel and a method of applying acoating thereto for reducing corrosion resulting from reaction withchemicals in chemically treated wood.

2. Description of the Prior Art

Construction hardware as used herein refers to various hangers,connectors, straps, tiedowns and the like which are used in theconstruction industry to connect wooden structural members to oneanother. Such construction hardware is commonly manufactured from rollsof coil steel. Many applications of such construction hardware are foruse in connection with wooden structural members comprised of lumbertreated with chemical preservatives (so called “treated lumber”).

Treated lumber is commonly used in outdoor structures exposed tomoisture and the environment to reduce deterioration of the lumber.Until a couple of years ago, the most common chemical preservative usedfor this purpose was a combination of chromium, copper and arsenic,namely chromated-copper-arsentate. This chemical preservative wascommonly referred to as “CCA”. For protection against atmospheric andother possible forms of corrosion, it was common throughout the industryto provide construction hardware with a protective coating of zinc or azinc alloy. Initially, such zinc coating was applied at a thickness ofG60 (0.6 oz. per square foot). More recently, to comply with variousforeign standards, the zinc coating has been applied at a thickness ofG90 (0.9 oz. per square foot). Thus, a G90 coating of zinc was believedto be a sufficient corrosion protector for construction hardware usedwith CCA treated lumber.

In part, due to the presence of arsenic in the CCA preservative, thewood treatment industry recently made a voluntary decision to eliminatearsenic from the preservative and thus moved away from CCA. The mostwidely recognized replacement wood preservative is a water based woodpreservative commonly referred to as ACQ comprising a combination ofcopper oxide and a quaternary ammonium compound. While treatment ofconstruction hardware with zinc at a thickness of G90 sufficientlyprotected CCA coated hardware from atmospheric and other various otherforms of corrosion, most test results suggested that ACQ treated lumberadded a further form of corrosion to construction hardware via adissimilar metal reaction between the copper and the zinc. The industryresponse to this increased corrosiveness was to provide constructionhardware with a thicker layer of zinc, namely, G185 (1.85 oz. per squarefoot). While this increased thickness of zinc functioned to extend theusable life of a piece of construction hardware from the destructivecorrosion of ACQ, the thicker zinc coating was still available to reactwith the copper in the ACQ treated lumber via a dissimilar metalreaction. Thus, increasing the zinc protective layer on the constructionhardware still involved a solution comprised of a sacrificial coatingmaterial. This necessarily resulted in a limited, but undetermined,useful product life.

Accordingly, there is a need in the art for construction hardware withalternate corrosion reducing properties and alternate methods ofreducing corrosion between construction hardware and preservativetreated lumber and particularly between construction hardware and ACQtreated lumber.

SUMMARY OF THE INVENTION

It is known that the underlying steel of zinc coated constructionhardware is protected against corrosion resulting from exposure tolumber treated with CCA by the zinc coating. The zinc coating iscommonly at a thickness of G60 or G90. Because lumber treated with ACQis considered to be more corrosive, the current process is to provide athicker layer of zinc as corrosion protection. However, ACQ containsunprotected copper which will react with the zinc in the zinc coatedhardware via a dissimilar metal reaction. Thus, the protection ofconstruction hardware against corrosion in ACQ treated lumber by zincalone, even thicker layers of zinc, is still a sacrificial protectiveprocess which will last only as long as the zinc remains unreacted withthe ACQ copper. Therefore, although thicker layers of zinc will providelonger protection against such corrosion, even the thicker layers ofzinc will ultimately be consumed and corrosion of the underlying steelwill occur.

In accordance with the present invention, the surface of zinc coatedconstruction hardware is isolated from the environment, mainly water andmoisture, thereby minimizing the dissimilar metal reaction between thezinc in the zinc coated hardware and the copper in the ACQ treatedlumber. More specifically, by applying a moisture barrier coating to azinc coated construction hardware member, reaction between the zinc andthe copper is minimized, thereby prolonging the life of the hardwarewithout increasing the thickness of the zinc.

Accordingly, an object of the present invention is to provide a methodof protecting construction hardware against corrosion by ACQ treatedlumber.

Another object of the present invention is to provide a method forreducing corrosion of construction hardware to ACQ treated lumberwithout increasing the protective zinc coating.

A still further object of the present invention is to provide an articleof construction hardware with a coating to protect against corrosion byACQ treated lumber.

These and other objects of the present invention will become apparentwith reference to the drawing, the description of the preferredembodiment and method and the appended claims.

DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of a portion of an article of constructionhardware showing the protective zinc and moisture barrier coatings,among others.

DESCRIPTION OF THE PREFERRED EMBODIMENT AND METHOD

The present invention relates generally to an article of constructionhardware provided with a coating to protect it against corrosion by ACQtreated lumber and a method for protecting an article of constructionhardware from such corrosion.

As a result of the wood preservative treatment industry moving away fromarsenic containing CCA treatment to the safer ACQ treatment, increasedcorrosion problems in construction hardware exposed to ACQ treatedlumber has occurred. Specifically, conventional zinc coatings of G60 andG90 thickness no longer provide sufficient corrosion protection.Accordingly, zinc coating thicknesses of G185 are being used. However,even these thicknesses are ultimately subject to degradation, and thuslack long term protective capability.

In accordance with the preferred method of the present invention,galvanized or zinc coated coil steel which has been coated on both sidesis provided in roll form. Preferably, this is zinc coated steel with azinc thickness of at least G60, more preferably G90. This steel iscommonly “chemically treated dry” to protect the coil of steel bypassivating the galvanization, or by reducing the chemical reactivity ofthe surface. However, because the specific moisture barrier coating ofthe preferred embodiment as discussed below does not adhere as well topassivated material, it is preferred that the galvanized steel betreated with light oil rather than being “chemically treated dry”.

In general, the present invention involves applying a moisture barriercoating or paint to both sides of zinc coated construction hardware, orto both sides of the roll material from which such hardware is made.This forms a substantially water/moisture barrier between the zinc andthe ambient atmosphere. By doing so, the dissimilar metal reactionbetween the zinc in the zinc coated hardware and the copper in the ACQtreated lumber, which would normally occur in construction hardwarecoated by zinc alone, is substantially reduced or eliminated.

This moisture or water barrier can be applied to a zinc coated roll ofcoil steel before manufacture of the individual hardware articles or canbe applied subsequent to manufacture or stamping of the individualhardware articles by dip coating or the like. The preferred embodiment,however, contemplates applying the moisture barrier coating to bothsides of a roll of zinc coated steel via a roll coating process or thelike and then forming the individual hardware pieces from the moisturebarrier coated coil steel. Preferably the forming is done in aconventional manner by stamping or the like.

A variety of moisture or water barrier coatings are acceptable for usein the present invention. Preferably, however, such moisture barriershould be a material which adheres to the outer surface of a zinc coatedconstruction hardware article despite the various bending, cutting andother steps involved in the manufacture of the hardware from the coilsteel. Further, the moisture or water barrier must preferably besufficient to substantially prevent water or moisture from contactingthe zinc coating on the hardware under normal use conditions.

Various moisture barriers have been considered for use in the presentinvention. In the preferred embodiment, the moisture coating is anorganic moisture barrier or coating selected from one or more of the 500Series of the family of Magni coatings. These are manufactured and soldby The Magni Group, Inc. of Birmingham, Mich. More specifically, themost preferred moisture barrier is a coating manufactured by The MagniGroup, Inc. and identified as Magni 599, or a variation thereof known asMagni L94. Magni L94 is an organic coating whose major chemicalingredient (in the amount of 30.0-32.0% wt.) is propylene glycolmonoethyl acetate (PMA). The Magni L94 coating may be applied via rollcoat or the like to a roll of coil steel or it may be applied toindividual construction hardware articles after manufacture. Preferably,the Magni L94 is applied to both sides of a roll at a dry film thicknessin the approximate range of 0.3 to 0.4 mil.

For many applications, the moisture barrier coating such as the MagniL94 coating adheres sufficiently to the zinc coating by itself, withoutfurther assistance. However, in other applications, adhesion of theMagni L94 to the zinc is an issue. Accordingly, a more preferredembodiment involves precoating the zinc coated steel with a pretreatmentchemical or conversion coating to improve adhesion between the zinc andthe moisture barrier coating. In the preferred method, this pretreatmentchemical is applied by reverse roll coating to the zinc at the beginningof the coil coating process. Preferably, the pretreatment chemical isone or more of the Bonderite family of conversion coating made and soldby the Henkel Technologies division of Henkel Corporation. Morespecifically, possible Bonderite family of chemicals include: Bonderite1402W, Bonderite 1455SF, Bonderite 1303 and Bonderite 1421-A. Thesechemicals are adhesion promoters which are preferably applied by reverseroll coating after cleaning and rinsing of the zinc coated steel andprior to oven drying. The pretreatment chemical is preferably applied atthe rate of about 11 to 16 milligrams (mg) per square foot (sf).

Because any moisture barrier coating, including Magni L94 of thepreferred embodiment, is susceptible to light scratching and rubbing tosome extent, a dry film lube (DFL) is added or applied to the steel coilafter the moisture barrier coating has been applied. Preferably, the dryfilm lubricant used in the preferred embodiment is Henkel Drawco DFL 767manufactured and sold by the Henkel Technologies division of HenkelCorporation. The applied DFL serves two functions. First, as indicatedabove, it assists in protecting the moisture barrier coating from lightscratches and rubbing. Second, it functions to lubricate the articlestamping equipment. Thus, when the DFL coating is used, the normal watersoluble lubricant which is typically applied to the steel to lubricatethe stamping equipment can be eliminated. In the preferred method, theDFL is applied by reverse roll coating at a rate of about 150 to 250milligrams (mg) per square foot (sf).

Accordingly, the method in accordance with the preferred embodiment ofthe present invention can be summarized as follows:

1. First, coil steel which has been zinc coated or galvanized on bothsides with the desired zinc thickness is provided. Preferably, this coilsteel comes treated with light oil to limit access to moisture and toprovide a better adhesion base than steel which has been chemicallytreated dry. The steel also has a zinc coating preferably no greaterthan G90.

2. Next, unless further coating steps are to be applied at the steelprovider, the coil is shipped or otherwise transferred to a precoatingfacility. Here the coil is unwound, cleaned and the coatings of thepretreatment chemical or conversion coating (Bonderite 1402W, 1455SF,1303 and/or 1421-A), the moisture barrier layer (Magni 599, Magni L94 orother organic moisture barrier) and the dry film lube (Henkel Drawco DFL767) are applied to both sides.

3. Next, the coil is slit into strips suitable for manufacture intoarticles of construction hardware in accordance with known procedures.Typical manufacturing procedures include stamping.

As shown in accompanying FIG. 1, the construction hardware in accordancewith the present invention comprises a piece of construction hardware 10which is coated with a protective layer 11 of zinc and which has alsobeen provided with a moisture barrier coating 12 on top of the zinc.Preferably, the zinc is of a thickness of at least G60, more preferablyG90. Preferably, the moisture barrier is selected from one of the Magnifamily of coatings, specifically Magni L94. A layer 14 of a chemicalpretreatment or conversion coating of an adhesion promoter such as theBonderite family of chemicals identified above is provided between thelayers 10 and 12 and a layer 15 of a dry film lube such as Henkel DrawcoDFL 767 is applied to the layer 12.

Although the description of the preferred embodiment is quite specific,it is contemplated that various modifications could be made withoutdeviating from the spirit of the present invention. Accordingly, it isintended that the scope of the present invention be dictated by theappended claims rather than by a description of the preferredembodiment.

1. A method of reducing ACQ wood preservative corrosion of an article ofconstruction hardware comprising: providing a roll of constructionhardware steel; applying a protective layer of zinc of at least G60thickness to said hardware steel; applying a moisture barrier coating tosaid protective layer of zinc; and manufacturing an article ofconstruction hardware from the coated steel.
 2. The method of claim 1wherein said moisture barrier layer is Magni L94.
 3. The method of claim1 including applying an adhesion promoting chemical pretreatment to saidprotective layer of zinc prior to applying said moisture barriercoating.
 4. The method of claim 3 wherein said chemical pretreatment isone of Bonderite 1402W, Bonderite 1455SF, Bonderite 1303 and Bonderite1421-A.
 5. The method of claim 1 wherein said protective zinc layer istreated with light oil prior to applying said chemical pretreatment. 6.The method of claim 1 including applying a dry film lube to saidmoisture barrier coating.
 7. The method of claim 6 wherein said dry filmlube is Henkel Drawco DFL
 767. 8. The method of claim 1 includingmanufacturing said article of construction hardware by stamping.
 9. Themethod of claim 2 including applying an adhesion promoting chemicalpretreatment to said protective layer of zinc prior to applying saidmoisture barrier coating wherein said chemical pretreatment is one ofBonderite 1402W, Bonderite 1455SF, Bonderite 1303 and Bonderite 1421-Aand including applying a dry film lube to said moisture barrier coatingwherein said dry film lube is Henkel Drawco DFL
 767. 10. A method ofreducing ACQ wood preservative corrosion of an article of constructionhardware comprising: providing a roll of zinc coated steel with a zincthickness of at least G60; forming an article of construction hardwarefrom said roll; and applying a moisture barrier coating to said articleover said zinc.
 11. The method of claim 10 wherein said moisture barrierlayer is Magni L94.
 12. The method of claim 10 including applying anadhesion promoting chemical pretreatment to said layer of zinc prior toapplying said moisture barrier coating.
 13. The method of claim 12wherein said chemical pretreatment is one of Bonderite 1402W, Bonderite1455SF, Bonderite 1303 and Bonderite 1421-A.
 14. The method of claim 13wherein said moisture barrier layer is Magni L94.
 15. An article ofconstruction hardware comprising: a base article of constructionhardware comprised of steel coated with zinc of at least G60 thicknessand a moisture barrier coating applied to said zinc.
 16. The article ofclaim 15 wherein said moisture barrier coating is Magni L94.
 17. Thearticle of claim 15 including an adhesion promoting chemicalpretreatment between said zinc and said moisture barrier coating. 18.The article of claim 15 including a coating of a dry film lube on saidmoisture barrier coating.
 19. The article of claim 16 including anadhesion promoting chemical pretreatment between said zinc and saidmoisture barrier coating and including a coating of a dry film lube onsaid moisture barrier coating.
 20. The article of claim 19 wherein saidchemical pretreatment is one of Bonderite 1402W, Bonderite 1455SF,Bonderite 1303 and Bonderite 1421-A and wherein said dry film lube isHenkel Drawco DFL 767.